Synthesis and hydrolysis of cationic palladium(II) 2,6-diacetylpyridine dimethyl ketal complexes. Cyclopalladation of 2,6-diacetylpyridine. Palladium-catalyzed synthesis of a 1,5-benzodiazepine

Article abstract of DOI:10.1021/om300217k

The complex [Pd(O¹,N¹,C¹-L)(OClO ₃)] (L = monoanionic ligand resulting from deprotonation of the acetyl group of the dimethyl monoketal of 2,6-diacetylpyridine) reacts with neutral ligands L¹ (phosphines, isocyanides, CO, N-donor ligands) to give the complexes [Pd(O¹,N¹,C¹-L)L ¹]ClO₄, [Pd(N¹,C¹-L)L ¹₂]ClO₄, and [Pd(C¹-L)L ¹₃]ClO₄. The complex [Pd(N¹,C ¹-L)(pda)]ClO₄ (pda = NH₂C₆H ₄NH₂-2) can be used as a catalyst for the synthesis of 2′,2′,4′-trimethyl-2′,3′-dihydro-1H-1′, 5′-benzodiazepine (Bzdiaz) from pda and acetone. The intermediate [Pd(O¹,N¹,C¹-L)(Bzdiaz)]ClO₄ has been isolated from an acetone solution of [Pd(N¹,C ¹-L)(pda)]ClO₄. The ligand L in some of the above complexes hydrolyzes to give [Pd(O¹,N¹,C ¹-L′)L¹]ClO₄ (L′ = monoanionic ligand resulting from the deprotonation of one acetyl group of 2,6-diacetylpyridine, L¹ = MeCN, ^tBuNC). These complexes are best prepared by reacting L¹ with [Pd(O¹,N ¹,C¹-L′)(NCMe)]ClO₄, which, in turn, can be obtained from 2,6-diacetylpyridinium perchlorate and Pd(OAc)₂ in MeCN. When THF is used as solvent, [Pd(O¹,N¹,C ¹-L′)(OH₂)]ClO₄ can be isolated. The crystal structures of [Pd(O¹,N¹,C¹-L′) (NCMe)]ClO₄ and [Pd(O¹,N¹,C¹-L) (CNXy)]ClO₄ have been determined.

Full text of DOI:10.1021/om300217k

Article
pubs.acs.org/Organometallics
Synthesis and Hydrolysis of Cationic Palladium(II) 2,6-
Diacetylpyridine Dimethyl Ketal Complexes. Cyclopalladation of 2,6-
Diacetylpyridine. Palladium-Catalyzed Synthesis of a 1,5-
Benzodiazepine†
Francisco Julia-Hernandez,‡ Aurelia Arcas,‡ Delia Bautista,§,∥ and Jose Vicente*,‡
́
́
́
‡Grupo de Química Organometal
́
ica, Departamento de Química Inorgan
́
ica, Facultad de Química, Universidad de Murcia, and §SAI,
Universidad de Murcia, Aptdo. 4021, E-30071 Murcia, Spain
S
* Supporting Information
ABSTRACT: The complex [Pd(O1,N1,C1-L)(OClO3)] (L = monoanionic
ligand resulting from deprotonation of the acetyl group of the dimethyl
monoketal of 2,6-diacetylpyridine) reacts with neutral ligands L1
(phosphines, isocyanides, CO, N-donor ligands) to give the complexes
[Pd(O1,N1,C1-L)L1]ClO4, [Pd(N1,C1-L)L1 ]ClO4, and [Pd(C1-L)L1 ]ClO4.
2
3
The complex [Pd(N1,C1-L)(pda)]ClO4 (pda = NH2C6H4NH2-2) can be
used as a catalyst for the synthesis of 2′,2′,4′-trimethyl-2′,3′-dihydro-1H-1′,5′-
benzodiazepine (Bzdiaz) from pda and acetone. The intermediate
[Pd(O1,N1,C1-L)(Bzdiaz)]ClO4 has been isolated from an acetone solution of [Pd(N1,C1-L)(pda)]ClO4. The ligand L in
some of the above complexes hydrolyzes to give [Pd(O1,N1,C1-L′)L1]ClO4 (L′ = monoanionic ligand resulting from the
deprotonation of one acetyl group of 2,6-diacetylpyridine, L1 = MeCN, tBuNC). These complexes are best prepared by reacting
L1 with [Pd(O1,N1,C1-L′)(NCMe)]ClO4, which, in turn, can be obtained from 2,6-diacetylpyridinium perchlorate and Pd(OAc)2
in MeCN. When THF is used as solvent, [Pd(O1,N1,C1-L′)(OH2)]ClO4 can be isolated. The crystal structures of [Pd(O1,N1,C1-
L′)(NCMe)]ClO4 and [Pd(O1,N1,C1-L)(CNXy)]ClO4 have been determined.
the deprotonation of one acetyl group of 2,6-diacetylpyridine;
Scheme 1) were shown to be precatalysts for some room-
temperature Heck-type reactions.13 The study of these
reactions allowed us to provide the first clear evidence of a
Pd(II)/Pd(IV) catalytic cycle,12,13 kinetic data proving that 3
was the best precatalyst, and a method for the isolation of
complex 3 from the catalytic mixture. This surprised us because,
as mentioned above, we unfruitfully attempted to prepare
homologues of 3 directly from palladium salts and dap (Scheme
1).
The above results showed the great promise of the pincer
complexes containing the ligands L and L′ and, at the same
time, the need for further work to prepare and study the
reactivity of derivatives 1−3. In this paper, we report (1) the
preparation of a family of cationic derivatives of 2, some of
which hydrolyze to give 3-type complexes, and (2) a direct
synthesis of 3 from dap, its reactivity, and its X-ray crystal
structure.
INTRODUCTION
■
Pd(II) ketonyl compounds of the type [Pd]CH2C(O)R1−3 are
interesting because of their stability, reactivity, and role as
intermediates in organic synthesis.4 We have reported the
synthesis and/or reactivity of ketonyl derivatives of other
metals, such as Pt,2,5 Au,6,7 Hg,3,5 and Tl.7,8 In this context, we
have recently described various attempts to prepare Pd(II)
ketonyl complexes derived from 2,6-diacetylpyridine (dap;
Scheme 1).9 However, they were unsuccessful, likely because of
the low nucleophilicity of this ligand, owing to the electron-
withdrawing nature of the two acetyl groups. It was only after
the ketalization of one these groups that metalation of the other
could be achieved. Both processes occurred when a MeOH
solution of PdCl2 and dap was refluxed, which allowed the
isolation of the pincer complex [Pd(O1,N1,C1-L)Cl] (1;
Scheme 1),9 where L is the monoanionic ligand resulting
from deprotonation of the acetyl methyl group in the
monoketal of 2,6-diacetylpyridine.
From complex 1 we have isolated some homologues9 and the
first family of Pd(IV) pincer complexes [Pd(O1,N1,C1-L)X3] (X
= Cl, Br,10 I;11 Scheme 1). Recently, we have reported the first
oxidative addition of an aryl halide to a palladium(II) complex,
which led to the synthesis of the Pd(IV) complex [Pd-
(O1,N1,C1-L)(C,O-C6H4CO2-2)I] (Scheme 1).12 The latter and
the Pd(II) derivatives [Pd(O1,N1,C1-L)(OAc)],12 [Pd-
(O1,N1,C1-L)(OClO3)] (2; Scheme 1), and [Pd(O1,N1,C1-
L′)(NCMe)]ClO4 (3; L′ = monoanionic ligand resulting from
RESULTS AND DISCUSSION
■
Synthesis of Cationic Complexes from [Pd(O1,N1,C1-
L)(OClO3)] (2). In the course of the study of the Heck
olefination of 2-iodobenzoic acid in acetone using 2 as
precatalyst,13 we observed the formation of the cationic
Received: March 16, 2012
Published: April 15, 2012
© 2012 American Chemical Society
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Monodentate ligands L1 reacted with 2, affording the
complexes [Pd(O1,N1,C1-L)L1]ClO4 (L1 = PPh3 (4), MeCN
Scheme 1
t
(5), mba (6), CO (7), BuNC (8), XyNC (9; Xy = C6H3Me2-
2,6); Scheme 2). One equivalent of L1 was used to prepare 4, 6,
Scheme 2
8, or 9. Dissolving solid 2 in MeCN or bubbling CO for 15 min
through a CHCl3 solution of 2 sufficed to prepare 5 or 7,
respectively.
The reaction of 2 with 2 equiv of RNC afforded [Pd(N1,C1-
L)(CNtBu)2]ClO4 (10) or equimolecular amounts of 9 and
[Pd(C1-L)(CNXy)3]ClO4 (11); however, when 3 equiv of
RNC was used, only the complex [Pd(C1-L)(CNR)3]ClO4 (R
solvento complex [Pd(O1,N1,C1-L)(S)]ClO4 (S = acetone; L =
monoanionic ligand resulting from deprotonation of the acetyl
group of the dimethyl monoketal of 2,6-diacetylpyridine) and
its slow hydrolysis to give MeOH and [Pd(O1,N1,C1-L′)(S)]-
ClO4 (L′ = monoanionic ligand resulting from the deprotona-
tion of one acetyl group of 2,6-diacetylpyridine). From the
mixture resulting at the end of the catalytic reaction we isolated
[Pd(O1,N1,C1-L′)(NCMe)]ClO4 (3) upon adding MeCN. As
we did not observe this hydrolysis in solutions of the complex
[Pd(O1,N1,C1-L)Cl] (1; Scheme 1) and its neutral homo-
logues,9 we concluded that the hydrolysis of [Pd(O1,N1,C1-
L)(S)]ClO4 in acetone occurred because of its cationic nature:
i.e., the increase in the acidic character of the metal center
favored the hydrolysis (see below). This explains that our
previous attempts to prepare cationic complexes from 1 gave
products that decomposed very easily at room temperature.
Therefore, to prepare the desired cationic complexes, we
reacted P-, N- or C-donor neutral ligands with CHCl3 or
CH2Cl2 solutions of 2 at short reaction times and temperatures
around 0 °C, in order to slow down the hydrolysis. The greater
stability of the cationic complexes resulting from 2 and primary
amines (H2NCH2C6H4OMe-4 = mba; o-phenylendiamine =
pda) or 1 equiv of XyNC allowed us to perform the reaction at
room temperature.
t
= Xy (11), Bu (12)) was obtained. We have reported that 1
reacts with isocyanides, giving at low temperature neutral
complexes resulting from coordination and insertion of RNC
into the Pd−C bond. When the temperature was raised, a
tautomerization process from β-ketoimine to β-ketoenamine
took place.9 This represents a significant difference with respect
to the reactions with 2, which we attribute to the reinforcement
of the C−Pd bond in the cationic complexes preventing the
insertion reaction. Recently, a similar behavior has been
reported in the migratory insertion of allyl groups across the
Pd−C bond in Pd(II) isocyanide complexes.14 One equivalent
of the bidentate ligand L2 gave the complexes [Pd(N1,C1-
L)L2]ClO4 (L2 = bis(diphenylphosphino)methane = dppm
(13), 4,4′-di-tert-butyl-2,2′-bipyridine = dbbpy (14), o-phenyl-
endiamine = pda (15); Scheme 3). When a 2:1 molar ratio of 2
and dppm was used, the dinuclear complex [Pd2(O1,N1,C1-
L)2(μ-dppm)](ClO4)2 (16) was obtained.
Reactivity of Cationic Complexes. Most of these cationic
complexes are stable at room temperature in the solid state
(exceptions are complexes 7, 11, and 12, which have to be
stored at approximately −30 °C) but, with the exception of 6
and 15, they hydrolyze or/and decompose in open-air
solutions. In most cases this transformation affords an
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Scheme 3
Scheme 4
irresolvable mixture of products but, in some cases, clean and
slow hydrolysis of the cationic complex was observed. Thus,
when a solution of 4 in CHCl3 was stirred in the open air for 24
h at room temperature, the complex [Pd(O1,N1,C1-L′)(PPh3)]-
ClO4 (17; Scheme 4) was quantitatively isolated as a stable
compound in the solid state and in solution. Similarly, a
solution of 5 in CHCl3 led after 15 days at room temperature to
3 (95% yield). In solution, the carbonyl complex 7 hydrolyzes,
loses CO, and decomposes, giving Pd metal. The hydrolysis of
1
8 was followed by H NMR in CDCl3. After 3 days, only 18
was detected, but it could not be isolated analytically pure from
the reaction mixture.
Complex 15 is insoluble in CH2Cl2 or CHCl3. When a
solution of 15 in acetone was stirred for 4 days at room
temperature, condensation of the amine ligand with the solvent
occurred, to give a good yield (85%) of the complex
[Pd(O1,N1,C1-L)(Bzdiaz)]ClO4 (19; Bzdiaz = 2′,2′,4′-trimeth-
yl-2′,3′-dihydro-1H-1′,5′-benzodiazepine coordinated through
N5′; Scheme 4), which is stable in the solid state and does
not hydrolyze in open air solutions. This cyclization reaction
probably occurs through a double condensation of acetone with
the diamine followed by an aldol-like addition (Scheme 4). As
far as we know, only a few 1,5-benzodiazepine complexes have
been reported,15−17 some of which have been used as catalysts
in ethylene oligomerization and polymerization.17 Only one is a
palladium complex,15 and all have been obtained by reacting a
metal complex with Bzdiaz. Therefore, 19 represents the first
example of a 1,5-benzodiazepine complex obtained by attack of
a ketone at the coordinated diamine. We have reported a
similar condensation process in the reaction of [Au(NH
CMe2)2]+ with NH3 and acetone.18
We have studied the use of complex 15 as a catalyst in the
reaction of pda with acetone. Thus, an acetone solution of pda,
in the presence of 5% of 15, gave a 96% yield of Bzdiaz, after 5
days at room temperature (Scheme 4). We have carried out
various experiments trying to optimize this process. However,
although lower concentrations of catalyst (1 or 5 mol %) at 50
°C improved the rate of the reaction, the 1,5-benzodiazepine
was obtained along with an unidentified by-product. The room-
temperature reaction with 1% catalyst gave only 5% conversion
after 22 h. In the absence of catalyst, the reaction afforded only
traces of Bzdiaz after 24 h and, after 10 days, a mixture, the
major component of which was Bzdiaz. It is reasonable to
assume that the catalytic cycle is closed when 19 reacts with
pda to give 15 (Scheme 4) and Bzdiaz. The most general
method for the synthesis of 1,5-benzodiazepines involves
condensation of o-phenylenediamine with α,β-unsaturated
carbonyl compounds, β-halo ketones, or ketones. Many
catalysts have been reported in the literature for this reaction.19
Antineuroinflammatory effects as well as anxiolytic and
cytotoxic against human cancer activities have been reported
for 1,5-benzodiazepines.20
We have described the synthesis of stable neutral complexes
containing the [Pd](O1,N1,C1-L), [Pd](N1,C1-L), and [Pd](C1-
L) moieties.9 However, all attempts to isolate the correspond-
ing complexes with the hydrolyzed L′ ligand by reacting the
stable O1,N1,C1-L′ complexes with neutral ligands were
unfruitful. Thus, the reaction of a CDCl3 solution of 18 with
t
1 equiv of BuNC did not afford the corresponding cis-
[Pd(N1,C1-L′)(CNtBu)2]ClO4 complex but metallic palladium
and a complex mixture of products in which free 2,6-
diacetylpyridine was identified. The same result was obtained
when 3 (Scheme 4) was reacted with 1 equiv of bpy (2,2′-
t
bipyridine) or dbbpy or with 2 equiv of BuNC.
Hydrolysis (deprotection) of ketals and acetals takes place by
reacting them with acids.21 Some metal salts or complexes have
also been used,22 the metal playing the role of a Lewis acid.
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Therefore, we assume that the cationic nature of complexes 4,
5, and 8 converts their metal center in a stronger acid than in
their neutral precursors facilitating the hydrolysis, as mentioned
above. We are not aware of any article reporting the hydrolysis
of a complex with a ketal or acetal ligand. However, several
works report the hydrolysis of cyclopalladated and -platinated
imines.23
The hydrolysis of the cationic complexes 4, 5, and 8 is a slow
process (Scheme 4). In the case of 5, we have found that the
amount of water (present in the solvent or added) does not
affect the rate of hydrolysis, being 14% after 14 h in acetone
solution. In contrast, if 10% HClO4 is added instead of water, a
quantitative yield of 3 was obtained after 40 min (see the
Experimental Section). This could mean that, although Pd(II)
activates the C−O(Me)Pd bond, a strong acid catalyst is
required to achieve a reasonable rate of hydrolysis.
derivatives of 2,6-diacetylpyridine. Thus, the best way to
prepare 17, first obtained from 4 (Scheme 4), is the reaction of
t
3 with PPh3 (Scheme 5). The reaction of 3 with BuNC (1:1)
was the only way we found to isolate pure complex 18 (98%
yield), because the hydrolysis of 8 led to a mixture from which
we could not separate 18.
Crystal Structures. The crystal structures of complexes 3
(Figure 1) and 9 (Figure 2) have been determined by X-ray
The Palladation of dap. Synthesis of 3 and Related
Complexes. Once we realized that complexes 3 and 17,
resulting from the hydrolysis of the cationic ketal derivatives,
were stable and isolable, we planned to retry the palladation of
dap. As we were aware that the low nucleophilicity of dap
prevents it from coordinating to Pd, which is essential to assist
palladation, we decided to attempt the reaction between 2,6-
diacetylpyridinium perchlorate, (Hdap)ClO4, and Pd(OAc)2 in
a weakly coordinating solvent, S. This way, we would generate
dap along with a highly electrophilic palladium compound
(“Pd(OAc)(ClO4)(S)n”), potentially capable of coordinating
dap and deprotonating it with its basic acetato ligand.
Fortunately, our expectation was met when we reacted a
THF suspension of (Hdap)ClO4 with 1 equiv of Pd(OAc)2 and
obtained [Pd(O1,N1,C1-L′)(OH2)]ClO4 (20; Scheme 5) in
Figure 1. Ellipsoid representation of 3 (50% probability). Selected
bond lengths (Å) and angles (deg): Pd(1)−N(1) = 1.9705(16),
Pd(1)−N(2) = 2.0072(17), Pd(1)−C(1) = 2.012(2), Pd(1)−O(1) =
2.2711(14), Pd(1)−Pd(1)#1 = 3.2179(3), N(1)−C(7) = 1.343(2),
C(7)−C(8) = 1.501(3), O(1)−C(8) = 1.232(2), O(2)−C(2) =
1.207(3); N(1)−Pd(1)−C(1) = 83.25(7), N(2)−Pd(1)−C(1) =
91.95(8), N(2)−Pd(1)−O(1) = 108.39(6), N(1)−Pd(1)−O(1) =
76.08(6), C(8)−O(1)−Pd(1) = 111.55(12), O(1)−C(8)−C(7) =
118.22(17), N(1)−C(7)−C(8) = 113.47(17), C(7)−N(1)−Pd(1) =
120.35(13).
Scheme 5
diffraction (Table 1, Supporting Information). Both show a
nearly square-planar coordination around the palladium atom
(mean deviation from the coordination plane: 0.0313 and
0.0292 Å for 3 and 9, respectively). In complex 3, the py ring
and the palladacycles PdNCCO and PdNCCC are almost
coplanar (the angles between the mean planes are 2.9 and 5.0°,
respectively), suggesting some electronic delocalization involv-
ing the pyC(Me)CO groups. The molecules are connected by
Pd···Pd (3.2179(3) Å) contacts (van der Waals radii of Pd: 2.05
Å),25 giving dimers with an inversion center. These dimers are
connected through nonclassical hydrogen-bonding interactions
C(11)−H(11A)···O(1), giving chains along the c axis. Anions
and cations are connected by two C−H···O hydrogen bonds,
giving altogether a complex 3D network. Both C−O distances
are significantly different (1.207(3) and 1.232(2) Å), being
longer, as expected, than the C−O(Pd) distance. The electronic
delocalization involving the pyC(Me)CO group forces the Pd−
O bond distance (2.2711(14) Å) to be longer than in 9
(2.2028(14) Å), in which, as expected, the PdNCCO ring is not
planar (Figure 2), the O(1) and C(8) atoms being −0.3286 and
+0.2157 Å, respectively, out of the plane formed by the pyridyl
ring and the palladium atom (mean deviation 0.0385 Å). In 9,
the XyNC ligand and the pyridine ring are almost coplanar
(subtended angle 11.3°). Anions and cations are connected by
two C−H···O4 hydrogen bonds, giving centrosymmetric
dimers. The cations are also interconnected by a C(9)−
almost quantitative yield (98%). Complex 20 can be stored in
the solid state at 4 °C under N2 but decomposes at room
temperature in the solid state or in acetone solution. When this
reaction was carried out in MeCN, complex 3 was isolated in
94% yield. The same synthetic strategy has been recently
applied to prepare ortho-palladated primary and secondary
amines, which had been previously obtained by less direct
methods or in lower yields.24
Complex 3, which is stable in the solid state and in solution,
is the best precursor for the synthesis of other palladated
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Scheme 6
Figure 2. Ellipsoid representation of 9 (50% probability). Hydrogen
atoms are omitted for clarity. Selected bond lengths (Å) and angles
(deg): Pd(1)−C(21) = 1.937(2), Pd(1)−N(1) = 1.9939(17), Pd(1)−
C(1) = 2.016(2), Pd(1)−O(1) = 2.2028(14), N(1)−C(7) = 1.336(3),
C(7)−C(8) = 1.527(3), O(1)−C(8) = 1.461(2), O(2)−C(2) =
1.213(2); C(21)−Pd(1)−C(1) = 91.24(8), N(1)−Pd(1)−C(1) =
83.42(8), N(1)−Pd(1)−O(1) = 76.22(6), C(21)−Pd(1)−O(1) =
109.18(7), C(8)−O(1)−Pd(1) = 112.24(11), O(1)−C(8)−C(7) =
105.21(16), N(1)−C(7)−C(8) = 116.37(18), C(7)−N(1)−Pd(1) =
120.76(14).
coordinated carbonyl group; these data are in agreement with
those obtained in the X-ray diffraction study of 3 (see above).
The band due to ν(CO) in the carbonyl complex 7 appears
at 2136 cm−1, only slightly below that in free CO (2143 cm−1),
as a result of the decreased π-donor ability of the palladium
atom in a cationic complex.26
CONCLUSION
■
Solutions of the complex [Pd(O1,N1,C1-L)(OClO3)], where L
is the monoanionic ligand resulting from deprotonation of the
acetyl group of the dimethyl monoketal of 2,6-diacetylpyridine,
have been used as starting material for the synthesis of cationic
dimethyl ketal complexes with the L ligand acting as pincer,
chelate (N1,C1-L), or terminal (C1-L). The complex [Pd(N1,C1-
L)(N,N-NH2C6H4NH2-2)]ClO4, which reacts with acetone to
afford a 1,5-benzodiazepine complex resulting from the
condensation of o-phenylenediamine with two molecules of
acetone, is a catalyst for the synthesis of 1,5-benzodiazepine
from o-phenylenediamine in acetone. Some of these cationic
complexes hydrolyze spontaneously to give MeOH and the
corresponding complexes with the pincer O1,N1,C1-L′ ligand (L′
= monoanionic ligand resulting from deprotonation of one
acetyl group of 2,6-diacetylpyridine). The complex [Pd-
(O1,N1,C1-L′)(NCMe)]ClO4, which can also be prepared by
metalation of 2,6-diacetylpyridine, provides another way to
prepare other complexes with the L′ ligand.
H(9A)···O(3) hydrogen bond, giving another centrosymmetric
dimer. All these nonclassical hydrogen bonds produce a double
chain. The Pd−N(1) bond distance is longer in 9 (1.9939 (17)
Å) than in 3 (1.9705(16) Å), showing the greater trans
influence of the C- with respect to the N-donor ligand.
Spectroscopic Properties. The low stability of some
complexes in solution prevented us from recording their
13C{1H} NMR spectra. The CH2 and MeO protons in those
complexes in which the ketal group is coordinated, 4−9, 16,
and 19, are equivalent at room temperature because of a fast
exchange between both MeO groups.9−12 This equivalence is
maintained in the other complexes in which the ketal group is
not coordinated. The isocyanides in complexes 10−12 are
equivalent probably because the neutral ligands are involved in
dissociation/reassociation processes, as shown in Scheme 6.
The exchange of RNC ligands can be slowed down at −60 °C
to see two types of isocyanides in the expected 1:1 (10) or 2:1
molar ratio (11, 12). At this temperature, 10 gives two broad
MeO resonances and a singlet for the CH2 protons, 11 shows a
singlet for the MeO and another for the CH2 protons, and 12
has a broad resonance including the MeO and CH2 protons.
Similarly, in the 1H NMR spectrum of 14 at room temperature,
the CH2 group gives a broad resonance and each of the tBu and
MeO protons shows a singlet, which suggests the existence of
the fast equilibrium shown in Scheme 6. At −60 °C they
resolve into two doublets (CH2) and two pairs of singlets (tBu
and MeO).
EXPERIMENTAL SECTION
■
General Procedures. Unless otherwise stated, the reactions were
carried out without precautions to exclude light or atmospheric oxygen
or moisture. Melting points were determined on a Reichert apparatus
and are uncorrected. Elemental analyses were carried out with a Carlo
Erba 1106 microanalyzer. IR spectra were recorded on a Perkin-Elmer
16F PC FT-IR spectrometer with Nujol mulls between polyethylene
sheets. NMR spectra were recorded on Bruker AC 200 and Avance
300 and 400 spectrometers. Chemical shifts were referenced to TMS
(1H, 13C) or H3PO4 (31P). When needed, NMR assignments were
performed with the help of APT, HMQC, and HMBC experiments.
Chart 1 shows the atom numbering used in NMR assignments. The
complex [Pd(O1,N1,C1-L)Cl] (1) was prepared as reported
The IR spectra of all complexes show an absorption in the
region 1652−1723 cm−1 corresponding to ν(CO) of the L or L′
ligands. Complexes with L′ ligands show also a band at lower
frequency (range 1636−1705 cm−1) assignable to ν(CO) of the
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ν(Cl−O) 1091. 1H NMR (200 MHz, CDCl3): δ 8.35 (t, 1 H, H4, 3JHH
= 7.8 Hz), 7.86 (dd, 1 H, H5, 3JHH = 7.8 Hz, 4JHH = 1.2 Hz), 7.77 (dd,
1 H, H3, 3JHH = 7.8 Hz, 4JHH = 1.2 Hz), 3.58 (s, 2 H, CH2), 3.49 (s, 6
H, OMe), 2.54 (br, 3 H, MeCN), 1.82 (s, 3H, Me). 13C NMR (50.30
MHz, CDCl3): δ 200.9 (s, CO), 158.6 (s, C7), 151.8 (s, C8), 142.6 (s,
C4), 127.7 (s, C5), 124.4 (s, C3), 123.3 (br, MeCN), 107.9 (s, C6),
52.8 (s, OMe), 35.7 (s, CH2), 25.0 (s, Me), 3.5 (s, NCCH3). Anal.
Calcd for C13H17N2O7ClPd: C, 34.30; H, 3.76; N, 6.15. Found: C,
34.22; H, 3.80; N, 6.05.
Chart 1
Synthesis of [Pd(O1,N1,C1-L)(NH2CH2C6H4OMe-4)]ClO4 (6). To
a solution of 2 (from 0.26 mmol of 1 and 0.51 mmol of AgClO4 in 10
mL of CH2Cl2) was added p-methoxybenzylamine (33.4 μL; 0.26
mmol) to give an orange solution that was stirred for 30 min.
Concentration (2 mL) and addition of Et2O (15 mL) gave a
suspension; the solid was filtered off, washed with Et2O, and air-dried
to give 6 as a pale orange solid. Yield: 138.1 mg, 97%. Mp: 125−126
°C. IR (cm−1): ν(N−H) 3247, ν(CO) 1694, ν(CN) 1610, ν(Cl−
O) 1030. 1H NMR (300 MHz, CDCl3): δ 8.20 (t, 1 H, H4, 3JHH = 7.8
Hz), 7.80 (dd, 1 H, H5 or H3, 3JHH = 7.8 Hz, 4JHH = 1.2 Hz), 7.61 (m,
3 H), 6.90 (m, 2 H), 3.87 (m, 2 H, NH2), 3.78 (s, 3 H, MeO), 3.69
previously.9 CHCl3 or CH2Cl2 solutions of [Pd(O1,N1,C1-L)(OClO3)]
(2)13 were obtained by reacting 1 with excess AgClO4.
Synthesis of (Hdap)ClO4. To a solution of 2,6-diacetylpyridine
(1.95 g, 11.95 mmol) in Et2O (40 mL) was slowly added HClO4
(70%, 1.54 mL, 17.92 mmol), and when the hot reaction mixture
reached room temperature, it was filtered. The solid was washed with
Et2O and then recrystallized in acetone (6 mL)/Et2O (30 mL) to give
(Hdap)ClO4 as a colorless solid. Yield: 97%. Mp: 121−122 °C. IR
(cm−1): ν(CO) 1723, ν(CN) 1617, ν(N−H) 3234, 3205, 3186,
1
ν(Cl−O) 1081. H NMR (400 MHz, acetone-d6): δ 9.10 (m, 1H, p-
1
H), 8.95 (m, 2H, m-H), 2.93 (s, 6H, 2 Me). H NMR (300 MHz,
2
(m, 2 H, CH2), 3.38 (s, 2 H, CH2Pd), 3.18 (s, 6 H, OMe), 1.65 (s, 3
MeCN-d3): δ 11.15 (br, 1H, NH), 9.14 (t, 1H, p-H, JHH = 7.8 Hz),
1
H, Me). H NMR (200 MHz, acetone-d6): δ 8.42 (t, 1 H, H4, 3JHH
=
8.83 (d, 2H, m-H, 2JHH = 7.8 Hz), 2.87 (s, 6H, Me). 13C NMR (75.45
MHz, MeCN-d3): δ 190.9 (s, CO), 153.5 (s, p-C), 143.2 (s, o-C),
131.3 (s, m-C), 26.6 (s, Me). Anal. Calcd for C9H10NO6Cl: C, 41.00;
H, 3.82; N, 5.31. Found: C, 41.07; H, 3.96; N, 5.67.
7.8 Hz), 7.91 (dd, 1 H, H3, 3JHH = 7.8 Hz, 4JHH = 1.2 Hz), 7.86 (dd, 1
H, H5, 3JHH = 7.8 Hz, 4JHH = 1.2 Hz), 7.70 (m, 2 H, o-amine), 6.98 (m,
2 H, m-amine), 4.31 (br, 2 H, NH2), 3.96 (m, 2 H, CH2), 3.79 (s, 3 H,
MeO), 3.45 (s, 2 H, CH2Pd), 3.27 (s, 6 H, OMe), 1.72 (s, 3 H, Me).
13C{1H} NMR (75.45 MHz, acetone-d6): δ 202.7 (C2), 160.8
(COMe), 159.0 (C7), 153.2 (C8), 142.8 (C4), 131.9 (o-CH), 131.6
(C−CH2), 128.3 (C3), 124.4 (C5), 115.0 (m-CH), 108.8 (C6), 55.7
(p-OMe), 52.5 (OMe), 49.4 (CH2NH2), 34.0 (CH2Pd), 25.1 (Me).
Anal. Calcd for C19H25N2O8ClPd: C, 41.39; H, 4.57; N, 5.08. Found:
C, 41.45; H, 4.64; N, 5.06.
Synthesis of [Pd(O1,N1,C1-L′)(NCMe)]ClO4 (3). Method a. To
a solution of (Hdap)ClO4 (894.2 mg, 3.39 mmol) in MeCN
(40 mL) was added Pd(OAc)2 (761.5 mg; 3.39 mmol). The
resulting solution was stirred for 40 min and then concentrated
to dryness. The resulting oil was dissolved in acetone (20 mL)
and the solution concentrated to dryness; this process was
carried out twice. The resulting solid was stirred with Et2O (2 ×
40 mL) in a water/ice bath until a suspension formed. It was
filtered under N2 and the resulting solid was washed with Et2O
and dried under a N2 stream, giving an orange solid that was
recrystallized in MeCN/Et2O to give 3 as a spectroscopically
pure solid.13 Yield: 94%.
Synthesis of [Pd(O1,N1,C1-L)(CO)]ClO4 (7). After CO was
bubbled into a solution of 2 (from 0.18 mmol of 1 and 0.55 mmol
of AgClO4 in 3 mL of CHCl3) for 15 min, colorless needles
crystallized. The solid was filtered off, washed with CHCl3, and air-
dried to give 7. Yield: 78%. Mp: 119−120 °C. IR (cm−1): ν(CO)
1
2136, ν(CO) 1709, ν(CN) 1599. H NMR (200 MHz, acetone-
Method b. To a solution of 5 (51.1 mg, 0.12 mmol) in acetone (5
mL) was added an aqueous solution of HClO4 (11.64 mol L−1, 1 μL,
0,012 mmol). The mixture was stirred for 40 min and then
concentrated (1 mL). Addition of Et2O (5 mL) gave a suspension
that was filtered, and the solid was washed with Et2O and air-dried to
give 3 as an orange solid. Yield: 94%.
d6): δ 8.62 (t, 1 H, H4, 3JHH = 8 Hz), 8.14 (dd, 1 H, H5 or H3, 3JHH
=
8 Hz, 4JHH = 1.2 Hz), 8.10 (dd, 1 H, H3 or H5, 3JHH = 8 Hz, 4JHH = 1.2
Hz), 4.04 (s, 2H, CH2), 3.65 (s, 6H, OMe), 1.90 (s, 3H, Me). Anal.
Calcd for C12H14NO8ClPd: C, 32.60; H, 3.19; N, 3.17. Found: C,
32.41; H, 3.05; N, 3.20.
Synthesis of [Pd(O1,N1,C1-L)(CNtBu)]ClO4 (8). To a cold
solution of 2 (from 0.15 mmol of 1 and 0.58 mmol of AgClO4 in 5
Synthesis of [Pd(O1,N1,C1-L)(PPh3)]ClO4 (4). To a cold solution
of 2 (from 0.05 mmol of 1 and 0.16 mmol of AgClO4 in 5 mL of
CHCl3, at 0 °C) was added PPh3 (13.9 mg; 0.05 mmol). The reaction
mixture was stirred for 40 min and concentrated (to 1 mL). Addition
of Et2O (5 mL) gave a suspension that was filtered, and the solid was
washed with Et2O and air-dried to give 4 as a pale yellow solid. Yield:
89%. Mp: 115−116 °C. IR (cm−1): ν(CO) 1699, ν(CN) 1600,
ν(Cl−O) 1094. 1H NMR (400 MHz, CDCl3): δ 8.33 (t, 1 H, H4, 3JHH
= 8 Hz), 7.94 (m, 1 H, H3), 7.84 (m, 1 H, H5), 7.78−7.68 (m, 6 H,
t
mL of CHCl3, at 0 °C) was added BuNC (645 μL, 226.2 mM
solution, 0.15 mmol). The solution was stirred for 20 min at 0 °C and
then concentrated to dryness. The residue was stirred in Et2O (10
mL) at 0 °C for 15 min and then filtered off. The solid was washed
with Et2O and air-dried to give 8 as a pale yellow solid. Yield: 89%.
Mp: 114−115 °C. IR (cm−1): ν(CN) 2213, ν(CO) 1705, ν(C
1
N) 1600, ν(Cl−O) 1093. H NMR (400 MHz, CDCl3): δ 8.39 (t, 1
H, H4, 3JHH = 7.6 Hz), 7.94 (dd, 1 H, H5 or H3, 3JHH = 7.6 Hz, 4JHH
=
3
PPh3), 7.62−7.50 (m, 9 H, PPh3), 3.19 (d, 2 H, CH2, JHP = 4 Hz),
1.2 Hz), 7.83 (dd, 1 H, H3 or H5, 3JHH = 7.6 Hz, 4JHH = 1.2 Hz), 3.55
(s, 2 H, CH2), 3.52 (s, 6 H, OMe), 1.84 (s, 3 H, Me), 1.62 (s, 9 H,
tBu). Anal. Calcd for C16H23N2O7ClPd: C, 38.65; H, 4.66; N, 5.63.
Found: C, 38.97; H, 4.61; N, 5.61.
3.05 (s, 6 H, OMe), 1.88 (s, 3 H, Me). 13C{1H} NMR (75.45 MHz,
3
CDCl3): δ 200.8 (s, CO), 157.1 (s, C7), 150.8 (d, JCP = 2 Hz, C8),
142.5 (s, C4), 134.0 (d, 2JCP = 13 Hz, o-CH, PPh3), 132.1 (d, 4JCP = 3
Hz, p-CH, PPh3), 129.5 (d, 3JCP = 11 Hz, m-CH, PPh3), 127.5 (d, 1JCP
4
Synthesis of [Pd(O1,N1,C1-L)(CNXy)]ClO4 (9). To a solution of 2
(from 0.01 mmol of 1 and 0.3 mmol of AgClO4 in 3 mL of CHCl3)
was added a solution of XyNC (13.0 mg, 0.01 mmol) in CHCl3 (1
mL). The reaction mixture was stirred for 2 h and then concentrated
(2 mL). The resulting solid was washed with CHCl3 and air-dried to
give 9 as a colorless solid. Yield: 88%. Mp: 210−211 °C. IR (cm−1):
= 51.5 Hz, Cipso), 127.3 (d, JCP2 = 3 Hz, C5), 124.2 (s, C3), 109.2 (s,
C6), 52.5 (s, OMe), 41.1 (d, JCP,cis = 5.3 Hz, CH2), 25.2 (s, Me).
31P{1H} NMR (162.29 MHz, CDCl3): δ 30.85. Anal. Calcd for
C29H29NO7ClPPd: C, 51.50; H, 4.32; N, 2.07. Found: C, 51.15; H,
4.45; N, 2.36.
Synthesis of [Pd(O1,N1,C1-L)(NCMe)]ClO4 (5). A solution of 2
(from 0.08 mmol of 1 and 0.31 mmol of AgClO4 in 4 mL of CHCl3)
was concentrated to dryness, and the resulting solid was dissolved in
MeCN (1 mL). After 5 min of stirring, the solution was concentrated
to dryness. The residue was vigorously stirred in Et2O (5 mL), the
resulting suspension was filtered, and the solid was washed with Et2O
and air-dried to give 5 as a pale yellow solid. Yield: 88%. Mp: 126−127
°C. IR (cm−1): ν(CN) 2295, ν(CO) 1703, ν(CN) 1600,
1
ν(CN) 2194, ν(CO) 1703, ν(CN) 1601, ν(Cl−O) 1080. H
3
NMR (400 MHz, acetone-d6): δ 8.59 (t, 1 H, H4, JHH = 8 Hz), 8.12
(dd, 1 H, H5 or H3, 3JHH = 8 Hz, 4JHH = 1.2 Hz), 8.08 (dd, 1 H, H3 or
3
4
3
H5, JHH = 8 Hz, JHH = 1.2 Hz), 7.44 (m, 1 H, p-H, Xy, JHH = 7.6
Hz), 7.29 (m, 2 H, m-H, Xy, 3JHH = 7.6 Hz), 3.78 (s, 2 H, CH2), 3.66
1
(s, 6 H, OMe), 2.52 (s, 6 H, Me, Xy), 1.93 (s, 3 H, Me). H NMR
(400 MHz, CD2Cl2): δ 8.41 (t, 1 H, H4, 3JHH = 8 Hz), 8.02 (dd, 1 H,
3741
dx.doi.org/10.1021/om300217k | Organometallics 2012, 31, 3736−3744

Organometallics
Article
H5 or H3, 3JHH = 8 Hz, 4JHH = 1.2 Hz), 7.87 (dd, 1 H, H3 or H5, 3JHH
89%. Mp: 172−173 °C. IR (cm−1): ν(CO) 1652, ν(CN) 1599,
ν(Cl−O) 1094. 1H NMR (400 MHz, CDCl3): δ 8.12 (t, 1 H, H4, 3JHH
= 8 Hz), 8.05−7.98 (m, 2 H, H5 + H3), 7.70−7.35 (m, 20 H, dppm),
4.43 (dd, 2 H, CH2, dppm, 2JHP = 12.4 Hz, 2JHP = 7.2 Hz), 3.32 (dd, 2
H, CH2, 3JHP,cis = 1.6 Hz, 3JHP,trans = 12 Hz), 2.81 (s, 6 H, OMe), 1.58
(s, 1.5 H, H2O), 1.39 (s, 3 H, Me). 31P{1H} NMR (162.29 MHz,
CDCl3): δ −2.83 (d, JPP = 206.4 Hz), −27.65 (d, JPP = 206.4 Hz).
Anal. Calcd for C36H36NO7ClPPd·0.75H2O: C, 53.25; H, 4.65; N,
1.72. Found: C, 53.11; H, 4.66; N, 1.64.
4
3
= 8 Hz, JHH = 1.2 Hz), 7.35 (m, 1 H, p-H, Xy, JHH = 7.6 Hz), 7.24
3
(m, 2 H, m-H, Xy, JHH = 7.6 Hz), 3.73 (s, 2 H, CH2), 3.56 (s, 6 H,
OMe), 2.48 (s, 6 H, Me, Xy), 1.88 (s, 3 H, Me). 1H NMR (200 MHz,
MeCN-d3): δ 8.37 (t, 1 H, H4, 3JHH = 8 Hz), 7.97 (dd, 1 H, H5 or H3,
4
3
3JHH = 8 Hz, JHH = 1.2 Hz), 7.89 (dd, 1 H, H3 or H5, JHH = 8 Hz,
4JHH = 1.2 Hz), 7.40 (m, 1 H, p-H, Xy, 3JHH = 7.6 Hz), 7.28 (d, 2 H, m-
H, Xy, 3JHH = 7.6 Hz), 3.65 (s, 2 H, CH2), 3.50 (s, 6 H, OMe), 2.48 (s,
6 H, Me, Xy), 1.80 (s, 3 H, Me). Anal. Calcd for C20H23N2O7ClPd: C,
44.05; H, 4.25; N, 5.14. Found: C, 44.02; H, 4.21; N, 5.15. Single
crystals were obtained by slow evaporation of the solvent of a solution
of 9 in CD2Cl2.
2
2
Synthesis of [Pd(N1,C1-L)(dbbpy)]ClO4·0.5H2O (14). To a
solution of 2 (from 0.08 mmol of 1 and 0.30 mmol of AgClO4 in 8
mL of CHCl3) was added dbbpy (4,4′-di-tert-butyl-2,2′-bipyridine, 20.1
mg, 0.08 mmol). The resulting solution was stirred at 0 °C for 30 min
and then concentrated to 1 mL. Addition of Et2O (3 mL) and n-
pentane (5 mL) gave a suspension; the solid was filtered off, washed
with n-pentane, and air-dried to give 14 as a yellow solid. Yield: 85%.
Mp: 258 °C dec. IR (cm−1): ν(CO) 1673, ν(CN) 1614, 1547,
Synthesis of cis-[Pd(N1,C1-L)(CNtBu)2]ClO4 (10). To a cold
solution of 2 (from 0.23 mmol of 1 and 0.92 mmol of AgClO4 in 7 mL
of CH2Cl2, at 0 °C) was added tBuNC (2 mL, 226.2 mM, 0.46 mmol).
The resulting solution was concentrated (2 mL, 0 °C), and Et2O (7
mL) was added. The mixture was vigorously stirred at 0 °C for 15 min,
and the solid was filtered off, washed with Et2O, and dried under N2 to
give 10 as a colorless solid. Yield: 98%. Mp: 95−96 °C. IR (cm−1):
ν(CN) 2242, 2214, ν(CO) 1677, ν(CN) 1602, ν(Cl−O)
1
ν(Cl−O) 1081. H NMR (400 MHz, CDCl3): δ 8.30 (br, 2 H, tbpy),
8.23 (t, 1 H, H4, 3JHH = 8 Hz), 8.17 (br, 2 H, tbpy), 7.90 (br, 2 H, H3
+ H5), 7.62 (dd, 2 H, tbpy, 3JHH = 5.6 Hz, 4JHH = 1.6 Hz), 3.70 (br, 2
H, CH2), 3.16 (s, 6 H, OMe), 1.82 (s, 3 H, Me), 1.59 (br, 1 H, H2O),
1.46 (s, 18 H, tBu). 1H NMR (400 MHz, CDCl3, −60 °C): δ 8.58 (d,
1
1093. H NMR (200 MHz, CDCl3): δ 8.30 (br, 1 H, H4), 7.96 (d, 1
3
3
H, H5 or H3, JHH = 8 Hz), 7.88 (d, 1 H, H3 or H5, JHH = 8 Hz),
3.00−3.80 (br, 8 H, CH2 + 2 MeO), 1.78 (br, 3 H, Me), 1.61 (br, 18
H, 2 tBu). 1H NMR (400 MHz, CDCl3, −60 °C): δ 8.38 (t, 1 H, H4,
3JHH = 8 Hz), 8.08 (d, 1 H, H5 or H3, 3JHH = 8 Hz), 8.00 (d, 1 H, H3
or H5, 3JHH = 8 Hz), 3.39 (br, 3 H, MeO), 3.28 (br, 3 H, MeO), 3.21
(s, 2 H, CH2), 1.73 (s, 3 H, Me), 1.70 (s, 9 H, tBu), 1.65 (s, 9 H, tBu).
Anal. Calcd for C21H32N3O7ClPd: C, 43.46; H, 5.56; N, 7.24. Found:
C, 43.21; H, 5.88; N, 7.31.
t
3
3
1H, bpy, JHH = 5 Hz), 8.37 (t, 1H, H4, JHH = 8 Hz), 8.22 (br, 1 H,
tbpy), 8.17 (br, 1 H, tbpy), 8.08 (d, 1 H, tbpy, 3JHH = 5 Hz), 7.98 (d, 1
H, H5 or H3, 3JHH = 8 Hz), 7.95 (d, 1 H, H3 or H5, 3JHH = 8 Hz), 7.68
(m, 2 H, tbpy), 4.36 (d, 1 H, CH2, 1JHH = 6.4 Hz), 3.36 (s, 3 H, MeO),
1
3.08 (d, 1 H, CH2, JHH = 6.4 Hz), 3.07 (s, 3 H, MeO), 1.81 (s, 3 H,
Me), 1.51 (s, 9 H, tBu), 1.46 (s, 9 H, tBu). Anal. Calcd for
C29H38N3O7ClPd·0.5H2O: C, 50.37; H, 5.68; N, 6.08. Found: C,
50.12; H, 5.85; N, 5.88.
Synthesis of [Pd(C1-L)(CNXy)3]ClO4·H2O (11). To a cold
solution of 2 (from 0.06 mmol of 1 and 0.19 mmol of AgClO4 in 3
mL of CHCl3, at 0 °C) was added a cold solution of XyNC (25.2 mg,
0.19 mmol) in CHCl3 (1 mL, at 0 °C). The resulting solution was
stirred for 20 min and concentrated to dryness at 0 °C, and the solid
was dissolved in CH2Cl2 (1 mL). Addition of Et2O (5 mL) gave a
suspension that was stored at −33 °C for 2 h. The solid was filtered
off, washed with Et2O, and air-dried to give 11 as a pale yellow solid.
Yield: 95%. Mp: 75−76 °C. IR (cm−1): ν(CN) 2196, 2184 (sh),
ν(CO) 1660, ν(CN) 1581, ν(Cl−O) 1091. 1H NMR (400 MHz,
CDCl3): δ 7.95−7.81 (m, 3 H, H3 + H4 + H5), 7.35 (t, 1 H, p-H, Xy,
Synthesis of [Pd(N1,C1-L)(N,N-NH2C6H4NH2-2)]ClO4·0.5H2O
(15). To a solution of 2 (from 0.39 mmol of 1 and 0.80 mmol of
AgClO4 in 10 mL of CH2Cl2) was added o-phenylidenediamine (42.3
mg; 0.39 mmol); the reaction mixture was stirred for 5 min and then
concentrated to 2 mL. Upon the addition of Et2O (8 mL) the
suspension that formed was filtered, and the solid was washed with
Et2O and air-dried to give 15 as a pale yellow solid. Yield: 201.7 mg,
97%. Mp: 175 °C dec. IR (cm−1): ν(N−H) 3302, ν(CO) 1654,
1
ν(CN) 1601, ν(Cl−O) 1076. H NMR (400 MHz, acetone-d6): δ
8.34 (t, 1 H, H4, 3JHH = 7.8 Hz), 8.13 (dd, 1 H, H5 or H3, 3JHH = 7.8
Hz, 4JHH = 1.2 Hz), 7.91 (dd, 1 H, H3 or H5, 3JHH = 7.8 Hz, 4JHH = 1.2
Hz), 7.49 (m, 2 H), 7.32−7.30 (m, 2 H), 6.67 (br, 2 H, NH2), 5.81
(br, 2 H, NH2), 3.38 (s, 6 H, OMe), 3.29 (s, 2 H, CH2), 2.84 (s, 1 H,
H2O), 2.13 (s, 3 H, Me). Anal. Calcd for C17H22N3O7ClPd·0.5H2O:
C, 38.43; H, 4.36; N, 7.91. Found: C, 38.50; H, 4.33; N, 7.91.
Synthesis of [Pd2(O1,N1,C1-L)2(μ-dppm)](ClO4)2 (16). To a
solution of 2 (from 0.24 mmol of 1 and 0.52 mmol of AgClO4 in 5 mL
of CH2Cl2) was added dppm (46.7 mg, 0.12 mmol). The mixture was
stirred for 4 h and then concentrated to 1 mL. Addition of Et2O (6
mL) gave an oil that was vigorously stirred in a water/ice bath. The
resulting suspension was filtered and the solid washed with Et2O and
air-dried to give 16 as an orange solid. Yield: 98%. Mp: 167−168 °C.
IR (cm−1): ν(CO) 1698, ν(CN) 1600, ν(Cl−O) 1094. 1H NMR
(400 MHz, CDCl3): δ 8.26 (t, 2 H, H4, 3JHH = 8 Hz), 7.90−7.80 (m,
3
3JHH = 7.6 Hz), 7.20 (d, 2 H, m-H, Xy, JHH = 7.6 Hz), 3.64 (s, 2 H,
CH2), 3.08 (s, 6 H, OMe), 2.46 (s, 18 H, Me, Xy), 1.65 (br, 1 H,
1
H2O), 1.55 (s, 3 H, Me). H NMR (400 MHz, CDCl3, −60 °C): δ
3
3
7.98 (d, 1 H, H5 or H3, JHH = 7.6 Hz), 7.93 (t, 1 H, H4, JHH = 7.6
Hz), 7.88 (d, 1 H, H3 or H5, 3JHH = 7.6 Hz), 7.44−7.41 (m, 3 H, p-H,
Xy), 7.30−7.22 (m, 6 H, m-H, Xy), 3.66 (s, 2 H, CH2), 3.06 (s, 6 H,
OMe), 2.50 (s, 12 H, Me, Xy), 2.49 (s, 6 H, Me, Xy), 1.51 (s, 3 H,
Me). Anal. Calcd for C38H41N4O7ClPd·H2O: C, 55.28; H, 5.25; N,
6.79. Found: C, 55.20; H, 5.15; N, 6.70.
Synthesis of [Pd(C1-L)(CNtBu)3]ClO4 (12). To a cold solution of
2 (from 0.14 mmol of 1 and 0.55 mmol of AgClO4 in 6 mL of CHCl3,
t
at 0 °C) was added BuNC (36.8 mg, 0.44 mmol); the solution was
stirred for 20 min and then concentrated to dryness. The residue was
crystallized in CH2Cl2/n-pentane and then filtered. The solid was
washed with n-pentane and air-dried to give 12 as a colorless solid.
Yield: 94%. Mp: 104−105 °C. IR (cm−1): ν(CN) 2222, ν(CO)
3
10 H, H5 or H3 and 8 H, dppm), 7.75 (dd, 2 H, H3 or H5, JHH = 8
2
Hz), 7.42−7.35 (m, 12 H, dppm), 3.96 (t, 2 H, CH2, dppm, JHP
=
10.8 Hz), 3.34 (d, 4 H, CH2, 3JHP = 3.6 Hz), 3.05 (s, 12 H, OMe), 1.82
(s, 6 H, Me). 31P{1H} NMR (162.29 MHz, CDCl3): δ 19.46 (s). Anal.
Calcd for C47H50N2O14Cl2P2Pd2: C, 46.55; H, 4.16; N, 2.31. Found:
C, 46.17; H, 4.56; N, 2.47.
1
1659, ν(CN) 1581, ν(Cl−O) 1092. H NMR (200 MHz, CDCl3):
δ 8.00−7.80 (m, 3 H, H3 + H4 + H5), 3.20 (s, 6 H, OMe), 3.14 (s, 2
H, CH2), 1.70 (s, 3 H, Me), 1.59 (s, 27 H, tBu). 1H NMR (400 MHz,
CDCl3, −60 °C): δ 8.04−7.86 (m, 3 H, H3 + H4 + H5), 3.21 (br, 8 H,
Synthesis of [Pd(O1,N1,C1-L′)(PPh3)]ClO4·H2O (17). Method
a. To a solution of 3 (61.2 mg; 0.15 mmol) in acetone (12 mL)
was added PPh3 (39.3 mg; 0.15 mmol). The solution was
stirred for 15 min and then concentrated to 2 mL. Addition of
Et2O (10 mL) gave a suspension that was stirred in an ice/
water bath for 10 min. The resulting suspension was filtered
and the solid washed with Et2O and air-dried to give 17 as an
orange solid. Yield: 83%.
t
OMe + CH2), 1.73 (s, 3 H, Me), 1.63 (s, 18 H, Bu), 1.62 (s, 9 H,
tBu). Anal. Calcd for C26H41N4O7ClPd: C, 47.07; H, 6.23; N, 8.44.
Found: C, 46.97; H, 6.27; N, 8.47.
Synthesis of [Pd(N1,C1-L)(dppm)]ClO4·0.75H2O (13). A mixture
of a cold solution of 2 (from 0.10 mmol of 1 and 0.31 mmol of
AgClO4 in 6 mL of CH2Cl2, at 0 °C) and dppm (39.4 mg; 0.10 mmol)
was stirred for 30 min and then concentrated to 1 mL. Addition of
Et2O (5 mL) led to a suspension that was filtered, and the solid was
washed with Et2O and air-dried to give 13 as a pale orange solid. Yield:
Method b. A solution of 4 (10.0 mg; 0.02 mmol) in CHCl3 (2 mL)
was stirred for 24 h and then concentrated (1 mL). Addition of Et2O
3742
dx.doi.org/10.1021/om300217k | Organometallics 2012, 31, 3736−3744

Organometallics
Article
(4 mL) gave a suspension that was stirred in a cool bath (0 °C) for 10
min. The resulting suspension was filtered and the solid washed with
Et2O and air-dried to give 17 as an orange solid. Yield: 93%. Mp: 161−
162 °C. IR (cm−1): ν(CO) 1708, 1636, ν(CN) 1595, ν(Cl−O)
1095. 1H NMR (400 MHz, CDCl3): δ 8.76 (m, 1 H, H5), 8.52 (t, 1 H,
H4, 3JHH = 8 Hz), 8.12 (m, 1 H, H3), 7.65−7.49 (m, 15H, PPh3), 3.17
0.03 mmol) in acetone (15 mL) was added o-phenylenediamine (72.5
mg, 0.67 mmol). The mixture was stirred at room temperature for 5
days, the solvent was evaporated, and Et2O was added (10 mL). The
suspension was filtered through a Celite plug, and the filtrate was
concentrated to dryness to give the spectroscopically pure 1,5-
1
benzodiazepine as a colorless solid. Yield: 96%. TON: 21. H NMR
3
(d, 2 H, CH2, JHP = 3.6 Hz), 3.07 (s, 3H, Me), 1.78 (s, 2 H, H2O).
(200 MHz, CDCl3):27 δ 7.14−6.69 (m, 4 H, Ar), 3.02 (br, 1 H, NH),
2.34 (s, 3 H, Me), 2.20 (s, 2 H, CH2), 1.31, (s, 6 H, 2 Me). Anal. Calcd
for C12H16N2: C, 76.55; H, 8.57; N, 14.88. Found: C, 76.23; H, 8.72;
N, 14.66.
13C{1H} NMR (100.81 MHz, CDCl3): δ 206.5 (s, C6), 200.5 (s, C2),
151.0 (d, C8, 3JCP = 2 Hz), 150.8 (d, C7, 3JCP = 2 Hz), 143.4 (s, C4),
133.9 (d, o-CH, PPh3, 2JCP = 12.7 Hz), 132.4 (s, C3), 131.9 (d, p-CH,
PPh3, 4JCP = 2.4 Hz), 129.4 (d, m-CH, PPh3, 3JCP = 11.4 Hz), 128.3 (d,
Synthesis of [Pd(O1,N1,C1-L′)(OH2)]ClO4 (20). To a suspension
of (Hdap)ClO4 (610.3 mg; 2.31 mmol) in THF (18 mL) was added
Pd(OAc)2 (519.7 mg; 2.31 mmol), and the mixture was stirred for 30
min to give a suspension (A) and an oil. The suspension A was
decanted, and the oil was vigorously stirred with Et2O (3 × 20 mL) for
20 min. The resulting solid was filtered off and dried with a N2 stream
to give orange 20. The suspension A was concentrated to dryness, and
the residue was ground with Et2O (20 mL) for 10 min and filtered off
under N2 to get a second crop of 20. Yield: 98%. Mp: 260 °C dec. IR
(cm−1): ν(H2O) 3371, ν(CO) 1721 (sh), 1705, ν(CN) 1570,
ν(Cl−O) 1089. 1H NMR (200 MHz, acetone-d6): δ 8.82 (dd, 1 H, H5
or H3, 3JHH = 7.8 Hz, 4JHH = 1.4 Hz), 8.68 (t, 1 H, H4, 3JHH = 7.8 Hz),
8.15 (dd, 1 H, H3 or H5, 3JHH = 7.8 Hz, 4JHH = 1.4 Hz), 3.66 (s, 2 H,
CH2), 3.07 (s, 3 H, Me), 3.05 (br, 2 H, H2O). Anal. Calcd for
C9H10NO7ClPd: C, 28.00; H, 2.61; N, 3.63. Found: 27.76; H, 2.75; N,
3.56.
1
2
Cipso, PPh3, JCP = 52.2 Hz), 127.9 (s, C5), 40.6 (d, CH2, JCP,cis= 4.8
Hz), 26.6 (s, Me). 31P{1H} NMR (162.29 MHz, CDCl3): δ 29.92 (s,
PPh3). Anal. Calcd for C27H23NO6ClPPd·H2O: C, 50.02; H, 3.89; N,
2.16. Found: C, 50.04; H, 3.60; N, 2.29.
Synthesis of [Pd(O1,N1,C1-L′)(CNtBu)]ClO4 (18). To a solution
t
of 3 (338.0 mg; 0.83 mmol) in MeCN (10 mL) was added BuNC
(93.4 μL; 0.83 mmol). The reaction mixture was stirred for 15 min
and concentrated to dryness. The residue was dissolved in CH2Cl2 (4
mL), and Et2O (8 mL) was added. The resulting suspension was
stirred at 0 °C for 30 min, and the solid was filtered off, washed with
Et2O, and air-dried. The resulting solid was treated with CH2Cl2 (10
mL) and filtered through Celite. The filtrate was concentrated (2 mL),
and Et2O (10 mL) was added. The suspension was filtered, and the
solid was washed with Et2O and air-dried to give 18 as a yellow solid.
Yield: 332.4 mg, 89%. Mp: 206 °C dec. IR (cm−1): ν(CN) 2218,
ν(CO) 1703, 1635, ν(CN) 1596, ν(Cl−O) 1086. 1H NMR (400
MHz, acetone-d6): δ 8.86 (dd, 1 H, H5, 3JHH = 7.8 Hz, 4JHH = 1.4 Hz),
X-ray Structure Determinations. Complexes 3 and 9 were
measured on a Bruker Smart APEX machine. The data were collected
using monochromated Mo Kα radiation in ω-scan. The structures
were solved by direct methods. All of the non-hydrogen atoms were
refined anisotropically on F2. The methyl groups were refined using
rigid groups and the other hydrogens in the riding mode.
3
3
8.74 (t, 1 H, H4, JHH = 7.8 Hz), 8.28 (dd, 1 H, H3, JHH = 7.8 Hz,
4JHH = 1.4 Hz), 3.69 (s, 2 H, CH2), 3.09 (s, 3H, Me), 1.67 (br, 9H,
tBu). H NMR (200 MHz, CDCl3): δ 8.67 (dd, 1 H, H5, JHH = 7.8
1
3
4
3
Hz, JHH = 1.2 Hz), 8.53 (t, 1 H, H4, JHH = 7.8 Hz), 8.12 (dd, 1 H,
3
4
H3, JHH = 7.8 Hz, JHH = 1.2 Hz), 3.61 (s, 2 H, CH2), 3.04 (s, 3H,
Me), 1.61 (br, 9H, Bu). 13C{1H} NMR (75.45 MHz, acetone-d6): δ
t
ASSOCIATED CONTENT
* Supporting Information
■
200.4 (s, C6), 152.9 (s, C8), 152.5 (s, C7), 144.6 (s, C4), 132.7 (s,
C3), 128.6 (s, C5), 35.0 (s, CH2), 29.9 (s, C(CH3)3), 26.5 (s, Me).
Anal. Calcd for C14H17N2O6ClPd: C, 37.27; H, 3.80; N, 6.21. Found:
C, 37.00; H, 3.84; N, 6.22.
S
CIF files and Table 1, giving crystal data for compounds 3 and
9. This material is available free of charge via the Internet at
http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*E-mail: jvs1@um.es. Web: http://www.um.es/gqo/.
■
Author Contributions
∥To whom correspondence regarding the X-ray diffraction
studies should be addressed. E-mail: dbc@um.es.
Notes
Synthesis of [Pd(O1,N1,C1-L)(Bzdiaz)]ClO4 (19). A suspension of
15 (164.0 mg, 0.31 mmol) in acetone (25 mL) was stirred for 4 days
and then concentrated to dryness. The residue was dissolved in
CH2Cl2 (2 mL), and Et2O (10 mL) was added. The solid was filtered
off, washed with Et2O, and air-dried to give 19 as a yellow solid. Yield:
160.3 mg, 85%. Mp: 134−135 °C. IR (cm−1): ν(N−H) 3322, ν(C
O) 1698, ν(CN) 1621, 1599, ν(Cl−O) 1079. 1H NMR (400 MHz,
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
We thank the Ministerio de Educacion
FEDER (Grant CTQ2007-60808/BQU), and Fundacio
■
́
y Ciencia (Spain),
́
n
́
Seneca (Grants 04539/GERM/06 and 03059/PI/05) for
financial support and a grant to F.J.-H.
CDCl3): δ 8.42 (t, 1 H, H4, 3JHH = 8 Hz), 7.90 (dd, 1 H, H10′, 3JHH
=
4
3
4
7.6 Hz, JHH = 1.2 Hz), 7.84 (dd, 1 H, H3, JHH = 8 Hz, JHH = 1.2
Hz), 7.74 (dd, 1 H, H5, 3JHH = 8 Hz, 4JHH = 1.2 Hz), 7.25−7.15 (m, 2
H, H8′ + H9′), 6.98 (dd, 1 H, H7′, 3JHH = 7.6 Hz, 4JHH = 1.2 Hz), 3.51
(br, 1 H, NH), 3.44 (s, 2 H, CH2), 3.23 (s, 6 H, MeO), 3.10 (s, 3 H,
MeC2′), 2.44 (s, 2 H, H3′), 1.75 (s, 3 H, Me), 1.40 (s, 6 H, MeC4′).
13C{1H} NMR (100.81 MHz, CDCl3): δ 201.7 (C2), 186.1 (C2′),
158.2 (C7), 152.1 (C8), 142.0 (C4), 139.3 (C11′), 138.9 (C6′), 129.1
(C9′), 127.3 (C5), 127.0 (C10′), 124.0 (C3), 123.7 (C7′), 123.2 (C8′),
108.1 (C6), 70.5 (C4′), 52.4 (OMe), 46.0 (C3′), 33.7 (CH2), 32.6
(NCMe), 30.0 (CMe2), 25.0 (Me). Anal. Calcd for
C23H30N3O7ClPd: C, 45.86; H, 5.02; N, 6.98. Found: C, 45.41; H,
5.39; N, 6.94.
REFERENCES
■
(1) Wanat, R. A.; Collum, D. B. Organometallics 1986, 5, 120.
Burkhardt, E. R.; Bergman, R. G.; Heathcock, C. H. Organometallics
1990, 9, 30. Veya, P.; Floriani, C.; Chiesi-Villa, A.; Rizzoli, C.
Organometallics 1993, 12, 4899. Vicente, J.; Abad, J. A.; Bergs, R.;
Jones, P. G.; Bautista, D. J. Chem. Soc., Dalton Trans. 1995, 3093.
́
Vicente, J.; Chicote, M. T.; Rubio, C.; Ramırez de Arellano, M. C.;
Jones, P. G. Organometallics 1999, 18, 2750. Vicente, J.; Arcas, A.;
Fernan
́ ́
dez-Hernandez, J. M.; Bautista, D. Organometallics 2001, 20,
2767. Culkin, D. A.; Hartwig, J. F. Organometallics 2004, 23, 3398.
́
́
Vicente, J.; Chicote, M. T.; Martınez-Martınez, J. A.; Jones, P. G.;
Bautista, D. Organometallics 2008, 27, 3254. Efimenko, I. A.;
Pd-Catalyzed Synthesis of 2′,2′,4′-Trimethyl-2′,3′-dihydro-
1H-1′,5′-benzodiazepine. To a solution of complex 15 (17.5 mg,
3743
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Organometallics
Article
Podobedov, R. E.; Shishilov, O. N.; Rezinkova, Y. N.; Churakov, A. V.;
Kuzmina, L. G.; Garbuzova, I. A.; Lokshin, B. V. Inorg. Chem. Commun.
2011, 14, 426.
(22) Balme, G.; Gore, J. J. Org. Chem. 1983, 48, 3336. Kantam, M. L.;
Neeraja, V.; Sreekanth, P. Catal. Commun. 2001, 2, 301. Lipshutz, B.
H.; Pollart, D.; Monforte, J.; Kotsuki, H. Tetrahedron Lett. 1985, 26,
705. Marcantoni, E.; Nobili, F.; Bartoli, G.; Bosco, M.; Sambri, L. J.
(2) Vicente, J.; Abad, J. A.; Chicote, M. T.; Abrisqueta, M.-D.; Lorca,
Org. Chem. 1997, 62, 4183. Marko,
B.; Plancher, J.-M.; Quesnel, Y.; Vanherck, J.-C. Angew. Chem., Int. Ed.
1999, 38, 3207. Maulide, N.; Vanherck, J.-C.; Gautier, A.; Marko, I. E.
́
I. E.; Ates, A.; Gautier, A.; Leroy,
́
J.-A.; Ramırez de Arellano, M. C. Organometallics 1998, 17, 1564.
(3) Vicente, J.; Arcas, A.; Fernandez-Hernandez, J. M.; Bautista, D.
Organometallics 2008, 27, 3978.
́
́
́
Acc. Chem. Res. 2007, 40, 381. Pluth, M. P.; Bergman, R. G.; Raymond,
K. N. Angew. Chem., Int. Ed. 2007, 46, 8587. Sen, S. E.; Roach, S. L.;
Boggs, J. K.; Ewing, G. J.; Magrath, J. J. Org. Chem. 1997, 62, 6684.
(23) Baar, C. R.; Jenkins, H. A.; Vittal, J. J.; Yap, G. P. A; Puddephatt,
R. J. Organometallics 1998, 17, 2805. Bonnet, L. G.; Douthwaite, R. E.;
Hodgson, R.; Houghton, J.; Kariuki, B. M.; Simonovic, S. Dalton Trans.
2004, 3528. Vicente, J.; Abad, J. A.; Lopez-Pelaez, B.; Martinez-
Viviente, E. Organometallics 2002, 21, 58. Vicente, J.; Abad, J. A.; Rink,
B.; Hernandez, F.-S.; Ramirez de Arellano, M. C. Organometallics
1997, 16, 5269.
(24) Vicente, J.; Saura-Llamas, I.; Oliva-Madrid, M. J.; Garcia-Lopez,
J. A. Organometallics 2011, 30, 4624.
(25) Batsanov, S. S. Inorg. Mater. 2001, 37, 871.
(26) Uson, R.; Fornies, J.; Martinez, R. J. Organomet. Chem. 1976,
112, 105. Vicente, J.; Arcas, A.; Borrachero, M. V.; Tiripicchio, A.;
Tiripicchio-Camellini, M. Organometallics 1991, 10, 3873.
(27) Sharma, S.; Prasad, D. N.; Singh, R. K. J. Chem. Pharm. Res.
2011, 3, 382. Jacob, R. G.; Radatz, C. S.; Rodrigues, M. B.; Alves, D.;
Perin, G.; Lenardao, E. J.; Savegnago, L. Heteroat. Chem. 2011, 22, 180.
(4) Cavinato, G.; Pasqualetto, M.; Ronchin, L.; Toniolo, L. J. Mol.
Catal. A: Chem. 1997, 125, 15. Chen, G. S.; Kwong, F. Y.; Chan, H. O.;
Yu, W. Y.; Chan, A. S. C. Chem. Commun. 2006, 1413. Sodeoka, M.;
Hamashima, Y. Bull. Chem. Soc. Jpn. 2005, 78, 941. Culkin, D. A.;
Hartwig, J. F. Acc. Chem. Res. 2003, 36, 234.
(5) Vicente, J.; Arcas, A.; Fernan
Masciocchi, N. Chem. Commun. 2005, 1267. Vicente, J.; Arcas, A.;
Fernandez-Hernandez, J. M.; D., B. Organometallics 2006, 25, 4404.
Vicente, J.; Arcas, A.; Fernan
Bautista, D. Organometallics 2007, 26, 6155.
(6) Vicente, J.; Bermudez, M. D.; Carrion
́ ́
dez-Hernandez, J. M.; Sironi, A.;
́
́
́
dez-Hernan
́
dez, J. M.; Aullon, G.;
́
, F. J. Inorg. Chim. Acta
́
1994, 220, 1. Vicente, J.; Bermudez, M. D.; Chicote, M. T.; San
́
chez-
Santano, M. J. J. Chem. Soc., Chem. Commun. 1989, 141. Vicente, J.;
Bermudez, M. D.; Carrillo, M. P.; Jones, P. G. J. Organomet. Chem.
́
́
1993, 456, 305. Vicente, J.; Bermudez, M. D.; Chicote, M. T.; San
Santano, M. J. J. Chem. Soc., Dalton Trans. 1990, 1945. Vicente, J.;
́
chez-
́
Bermudez, M. D.; Escribano, J.; Carrillo, M. P.; Jones, P. G. J. Chem.
́
Soc., Dalton Trans. 1990, 3083.
(7) Vicente, J.; Abad, J. A.; Cara, G.; Gutierrez-Jugo, J. F. J. Chem.
Soc., Dalton Trans. 1992, 2481.
(8) Vicente, J.; Abad, J. A.; Cara, G.; Jones, P. G. Angew. Chem., Int.
Ed. Engl. 1990, 29, 1125.
(9) Vicente, J.; Arcas, A.; Julia-
Organometallics 2010, 29, 3066.
́
́
Hernandez, F.; Bautista, D.
(10) Vicente, J.; Arcas, A.; Julia-
Commun. 2010, 46, 7253.
́
Hernan
Hernan
Hernan
́
dez, F.; Bautista, D. Chem.
(11) Vicente, J.; Arcas, A.; Julia-
́
́
dez, F.; Bautista, D. Inorg.
dez, F.; Bautista, D. Angew.
Chem. 2011, 50, 5339.
(12) Vicente, J.; Arcas, A.; Julia-
́
́
Chem., Int. Ed. 2011, 50, 6896.
(13) Vicente, J.; Arcas, A.; Julia-
in press.
́ ́
Hernandez, F. Chem. Eur. J. 2012, 18,
(14) Canovese, L.; Visentin, F.; Santo, C.; Levi, C. Organometallics
2009, 28, 6762.
(15) Aversa, M. C.; Giannetto, P.; Bruno, G.; Cusumano, M.;
Giannetto, A.; Geremia, S. J. Chem. Soc., Dalton Trans. 1990, 2433.
(16) Aversa, M. C.; Bonaccorsi, P.; Cusumano, M.; Giannetto, P.;
Minniti, D. J. Chem. Soc., Dalton Trans. 1991, 3431. Samanta, U.;
Chakrabarti, P.; Naskar, J. P.; Hati, S.; Datta, D. Indian J. Chem., Sect. A
1999, 38A, 553.
(17) Zhang, S.; Vystorop, I.; Tang, Z.; Sun, W. H. Organometallics
2007, 26, 2456. Zhang, S.; Sun, W.-H.; Kuang, X.; Vystorop, I.; Yi, J. J.
Organomet. Chem. 2007, 692, 5307.
(18) Vicente, J.; Chicote, M. T.; Guerrero, R.; Ramirez de Arellano,
M. C. Chem. Commun. 1999, 1541. Vicente, J.; Chicote, M. T.;
Guerrero, R.; Saura-Llamas, I. M.; Jones, P. G.; Ramirez de Arellano,
M. C. Chem. Eur. J. 2001, 7, 638.
(19) For some recent examples see: More, U. B.; Kharat, R. S.;
Mahulikar, P. P. Asian J. Chem. 2011, 23, 4311. Nardi, M.; Cozza, A.;
Maiuolo, L.; Oliverio, M.; Procopio, A. Tetrahedron Lett. 2011, 52,
4827. Radatz, C. S.; Silva, R. B.; Perin, G.; Lenardao, E. J.; Jacob, R. G.;
Alves, D. Tetrahedron Lett. 2011, 52, 4132 and references therein..
(20) Ha, S. K.; Shobha, D.; Moon, E.; Chari, M. A.; Mukkanti, K.;
Kim, S.-H.; Ahn, K.-H.; Kim, S. Y. Bioorg. Med. Chem. Lett. 2010, 20,
3969. Chatterjee, N. R.; Chandak, B. G.; Thube, S. S.; Kulkarni, S. D.;
Deshpande, A. D. Int. J. Chem. Sci. 2009, 7, 805. Nawrocka, W.; Sztuba,
B.; Opolski, A.; Wietrzyk, J.; Kowalska, M. W.; Glowiak, T. Archiv
Pharm. 2001, 334, 3.
(21) Colvin, E. W.; Raphael, R. A.; Roberts, J. S. J. Chem. Soc., Chem.
Commun. 1971, 858. Ellison, R. A.; Lukenbach, E. R.; Chiu, C.-W.
Tetrahedron Lett. 1975, 16, 499.
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